Gas Phase Enhancement of Emission Color Quality in Solid State LEDs

ABSTRACT

Light-emitting materials are made from a porous light-emitting semiconductor having quantum dots (QDs) disposed within the pores. According to some embodiments, the QDs have diameters that are essentially equal in size to the width of the pores. The QDs are formed in the pores by exposing the porous semiconductor to gaseous QD precursor compounds, which react within the pores to yield QDs. According to certain embodiments, the pore size limits the size of the QDs produced by the gas-phase reactions. The QDs absorb light emitted by the light-emitting semiconductor material and reemit light at a longer wavelength than the absorbed light, thereby “down-converting” light from the semiconductor material.

FIELD OF THE INVENTION

This application relates to gas phase synthesis of nanoparticle-basedmaterials. More particularly, but not exclusively, it relates todown-converting light from a light emitting diode (LED) by synthesizingQDs within pores etched into the LED.

BACKGROUND

There has been substantial interest in exploiting compoundsemiconductors having particle dimensions on the order of 2-50 nm, oftenreferred to as quantum dots (QDs), nanoparticles, and/or nanocrystals.These materials have high commercial interest due to their size-tunableelectronic properties, which can be exploited in a broad range ofcommercial applications. Such applications include optical andelectronic devices, biological labeling, photovoltaics, catalysis,biological imaging, light emitting diodes (LEDs), general spacelighting, and electroluminescent displays.

Well-known QDs are nanoparticles of metal chalcogenides (e.g, CdSe orZnS). Less studied nanoparticles include III-V materials, such as InP,and including compositionally graded and alloyed dots. QDs typicallyrange from 2 to 10 nanometers in diameter (about the width of 50 atoms),but may be larger, for example up to about 100 nanometers. Because oftheir small size, QDs display unique optical and electrical propertiesthat are different in character to those of the corresponding bulkmaterial. The most immediately apparent optical property is the emissionof photons under excitation. The wavelength of these photon emissionsdepends on the size of the QD.

The ability to precisely control QD size enables a manufacturer todetermine the wavelength of its emission, which in turn determines thecolor of light the human eye perceives. QDs may therefore be “tuned”during production to emit a desired light color. The ability to controlor “tune” the emission from the QD by changing its core size is calledthe “size quantization effect”. The smaller the QD, the higher theenergy, i.e. the more “blue” its emission. Likewise, larger QDs emitlight more toward the electromagnetic spectrum's red end. QDs may evenbe tuned beyond visible spectrum, into the infrared or ultra-violetbands. Once synthesized, QDs are typically either in powder or solutionform.

A particularly attractive application for QDs is in the development ofnext generation LEDs. LEDs are becoming increasingly important in modernday life and it's predicted that they have the potential to become amajor target for QD applications. QDs can enhance LEDs in a number ofareas, including automobile lighting, traffic signals, general lighting,liquid crystal display (LCD) backlight units (BLUs), and displayscreens.

Currently, LED devices are typically made from inorganic solid-statecompound semiconductors, such as GaN (blue), AlGaAs (red), AlGaInP(orange-yellow-green), and AlGaInN (green-blue). Each of these materialsemit a single color of light, as indicated. As white light is a mixtureof colors in the spectrum, solid-state LEDs that emit white light cannotbe produced using a single solid-state material. Moreover, it isdifficult to produce “pure” colors by combining solid-state LEDs thatemit at different frequencies. At present, the primary method ofproducing white light or a mixture of colors from a single LED is to“down-convert” light emitted from the LED using a phosphorescentmaterial on top of the solid-state LED. In such a configuration, thelight from the LED (the “primary light”) is absorbed by thephosphorescent material and re-emitted at a second, lower frequency (the“secondary light”). In other words, the phosphorescent materialsdown-converts the primary light to secondary light. The total lightemitted from the system is a combination of the primary and secondarylight. White LEDs produced by phosphor down-conversion cost less and aresimpler to fabricate than combinations of solid-state red-green-blueLEDs. Unfortunately, however, conventional phosphor technology produceslight with poor color rendering (i.e. a color rendering index (CRI)<75).

QDs are a promising alternative to conventional phosphor technology.Their emission wavelength can be tuned by manipulating nanoparticlesize. Also, so long as the QDs are monodispersed, they exhibit strongabsorption properties, narrow emission bandwidth, and low scattering.Rudimentary QD-based light-emitting devices have been manufactured byembedding coloidally produced QDs in an optically transparent (orsufficiently transparent) LED encapsulation medium, such a silicone oran acrylate, which is then placed on top of a solid-state LED. Thus, thelight produced from the LED package is a combination of the LED primarylight and the secondary light emitted from the QD material.

However, such systems are complicated by the nature of current LEDencapsulants. For example, QDs can agglomerate when formulated intocurrent LED encapsulants, thereby reducing their optical performance.Furthermore, even after the QDs have been incorporated into the LEDencapsulant, oxygen can still migrate through the encapsulant to thesurfaces of the QDs, which can lead to photo-oxidation and, as a result,a drop in quantum yield (QY).

Thus, there is need in the art for a fast and inexpensive method thatcan reliably down-convert an LED.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description,will be better understood when read in conjunction with the appendeddrawings. For the purpose of illustration only, there is shown in thedrawings certain embodiments. It's understood, however, that theinventive concepts disclosed herein are not limited to the precisearrangements and instrumentalities shown in the figures.

FIGS. 1A-1C illustrate pores etched into a semiconductor material.

FIG. 2 shows the formation of QDs within pores of a semiconductormaterial from gaseous precursors provided with counter current gasstreams.

FIG. 3 shows the formation of QDs within pores of a semiconductormaterial from gaseous precursors provided with parallel gas streams.

FIG. 4 illustrates an apparatus for providing counter-current flow of QDprecursor gases.

FIG. 5 illustrates an apparatus for providing parallel flow of QDprecursor gases.

FIG. 6 is a diagram comparing the relative size of an oxygen molecule togas-phase precursor molecules of QDs.

FIGS. 7A-7C illustrate the formation of QDs within pores selectivelyetched into a semiconductor material.

FIG. 8 illustrates a conventional LED having nanoparticles embeddedwithin a porous n-GaN layer.

DESCRIPTION

It should be understood that the inventive concepts set forth herein arenot limited in their application to the construction details orcomponent arrangements set forth in the following description orillustrated in the drawings. It should also be understood that thephraseology and terminology employed herein are merely for descriptivepurposes and should not be considered limiting. It should further beunderstood that any one of the described features may be used separatelyor in combination with other features. Other invented systems, methods,features, and advantages will be or become apparent to one with skill inthe art upon examining the drawings and the detailed description herein.It is intended that all such additional systems, methods, features, andadvantages be protected by the accompanying claims.

The present disclosure generally relates to light emitting devices usinga solid-state LED material into which pores have been etched. QDs aresynthesized within those pores. When the LED material emits light (i.e.,primary light) the QDs absorb some of that light and reemit light havinga color determined by the size of the QDs (i.e., secondary light). Thelight emitted from the light-emitting device therefore includes acombination of the primary and secondary light. Various combinations ofLED materials and QD materials and sizes can be used to obtain whitelight or to obtain other blends of light.

According to some embodiments, the QD materials are synthesized withinthe pores of the LED material via gas phase reactions. As explained inmore detail below, the gas phase QD precursor material diffuse into thepores of the LED material where they react to form QDs. The size of theQDs may be limited by the size of the pores in which the QDs form. Inthis way, the pores may be thought of as providing a “template” for QDformation. Since the color of light that a QD emits depends on the sizeof the QD, the color of emitted light can be tuned by controlling thesize of the pores in which the QDs form.

Generally, any solid-state LED semiconductor material can be used.Examples include, but are not restricted to, inorganic solid-statecompound semiconductors, such as GaN (blue), AlGaAs (red), AlGaInP(orange-yellow-green), AlGaInN (green-blue), or any derivatives thereof.The characteristic emission colors of each material are provided inparentheses. The examples discussed in this disclosure primarily concernGaN, as it is common to seek to down-convert light from blue-emittingGaN.

Pores can be etched in the solid-state LED semiconductor material usingany means known in the art. Examples of controlled etching are containedin Cuong Dang et al., A wavelength engineered emitter incorporatingCdSe-based colloidal quantum dots into nanoporous InGaN/GaN multiplequantum well matrix, Phys. Status Solidi, No. 7-8, 2337-339 (2011); Danget al., A wafer-level integrated white-light-emitting diodeincorporating colloidal quantum dots as a nanocomposite luminescentmaterial, Adv. Materials, No. 24, 5915-18 (2012); and Chen et al., Highreflectance membrane-based distributed Bragg reflectors for GaNphotonics, App. Phys. Lett., No. 101, 221104 (2012). The reader isreferred to those references for details concerning the etching of theLED semiconductor material. Generally, the LED semiconductor material isetched using an electrochemical method, for example, anodic etching inan oxalic acid electrolyte. The pore size and concentration can becontrolled as a function of the applied voltage. Other methods ofetching, such as acid etching and/or inductively coupled plasma-reactiveion (ICP-RI) etching may be used. It is found that the etching techniquedoes not impair the semiconductor material's carrier transport andrecombination capability. FIGS. 1A-1B, by way of example only,illustrate semiconductor materials having etched pores.

In some embodiments, the etching technique produces pores havingapproximately the same diameter. For example, referring to FIG. 1A, thepores 100 can be etched to a target pore size. In one embodiment, thetarget pore size may be between approximately 2 nm and 10 nm. The poresize can be tuned to a uniform diameter that accommodates growth of bothred-emitting QDs and green-emitting QDs. For example, the pore size canbe tuned to a single diameter that accommodates growth of red-emittingGroup III-V based QDs (e.g. InP, and including graded dots and alloys),and green-emitting CdSe QDs. In one embodiment, a semiconductor materialfor a blue-LED (e.g., GaN) is selectively etched as in FIG. 1A toaccommodate growth of both red and green QDs at a level that effectivelydown-converts the LED to produce white light emissions.

Alternatively, the semiconductor material can be selectively etched toinclude pores of various sizes, as shown in FIG. 1B, 110, 120. Forexample, a semiconductor material for a blue-LED (e.g., GaN) can beselectively etched as in FIG. 1B to accommodate growth of both red andgreen QDs at a level that effectively down-converts the LED to producewhite light emissions.

In other embodiments, as illustrated in FIG. 1C, the etching techniqueproduces pores 130 having a small diameter on the top side of asemiconductor material, and pores 140 having a large diameter on thebottom side of the semiconductor material. For example, the bottom sideof the semiconductor material can be etched first to a target depth(e.g., halfway) and pore size (e.g., larger diameter). Etching time cancontrol the pore depth, while changing the bias voltage can control thepore size. After etching large pores 140 into the bottom layer, thesemiconductor material can be turned over, and small pores 130 can beselectively etched in the top layer to a target depth (e.g., halfway)and pore size (e.g., smaller diameter). Again, etching time and biasvoltage can be used to control pore depth and size. According to someembodiments, the small diameter pores 130 are etched to a size that canaccommodate growth of green QDs and the large diameter pores 140 areetched to a size that can accommodate growth of red QDs. This porearchitecture positions the red QDs below the green QDs to preventreabsorption of the secondary light emitted by the QDs. In oneembodiment, a semiconductor material for a blue-LED (e.g., GaN) isselectively etched as in FIG. 1C to accommodate growth of both red andgreen QDs at a level that effectively down-converts the LED light toproduce white light.

Once the LED semiconductor material is etched to provide pores, QDs areformed within those pores by reacting gas phase QD precursor compoundstogether within the pores. The precursors may be used to synthesize QDsincluding, but not restricted to, the following materials: Group II-VInanoparticles (e.g., CdS, CdSe, ZnS, ZnSe), Group III-V nanoparticles(e.g., InP, GaP), Group II-V nanoparticles (e.g., Cd₃P₂), and GroupIII-VI nanoparticles (e.g., In₂Se₃). In one embodiment, suitablegas-phase precursors may include, but are not restricted to, a Group IIor Group III cation source, (e.g., R₂Cd/Zn; R₃Ga/In (R=organic group)),and a Group V or Group VI anion source, (e.g., H₂S, H₂Se or H₃P). In yetanother embodiment, the flow rate of the gas-phase precursors may becontrolled using a carrier gas. The carrier gas may include, but is notlimited to, an inert gas (e.g., He, N₂ or Ar), or a reducing gas (e.g.,H₂).

The pores in the semiconductor material allow the gas phase precursorsto diffuse throughout the material. The nucleation and growth of QDsfrom gaseous precursors may proceed in any pores. Furthermore, since QDstability increases with particle size, under suitable reactionconditions particle growth may continue until all the space is occupied.Therefore, the size of the nanoparticles can be restricted by the porediameter. By way of example only, QDs having an approximately 5 nmdiameter can form in approximately 5 nm pores. In one embodiment, QDshaving uniform dimensions can grow in the pores. In another embodiment,QDs having variable diameters grow in the pores. In one embodiment, bothred and green QDs grow in the pores of a semiconductor material for ablue-LED (e.g., GaN) at a level that effectively down-converts the LEDto produce white light emissions. The resulting material is free ofliquid solvents because the QD-producing reactions involve only gasphase precursors.

QDs may be prepared by the reaction of gas phase QD precursors asdescribed in N. L. Pickett et al., in J. Mater. Chem., 1997, 7, 1855 andin J. Mater. Chem., 1996, 6, 507. The size of the resultant QDs may bevaried by careful control of the reaction conditions (e.g., temperature,time, etc.), and the addition of pyridine in the gas phase. Likewise,the methods used to synthesize QDs in polymer matrices described byHaggata et al. S. W. Haggata et al., J. Mater. Chem., 1996, 6, 1771 andJ. Mater. Chem., 1997, 7, 1996 may be adapted to synthesize QDs in thepores of the LED semiconductor material. The Pickett and Haggatareferences cited in this paragraph are hereby incorporated by referencein their entirety.

Generally, the gas phase QD precursors are exposed to the pores inparallel or counter flow and allowed to react within the pores. In oneembodiment, the pores have variable sizes to accommodate both red andgreen QD growth. In another embodiment, the reaction conditions arecontrolled to produce both red and green QDs. In yet another embodiment,the QDs may be formed in the semiconductor material at a level thateffectively down-converts the semiconductor material to produce whitelight emissions.

Gas phase reaction conditions can be used to control QD growth withinthe semiconductor material. For example, pyridine and highertemperatures may be used to inhibit nanoparticle growth as reported byPickett et al., Effect of pyridine upon gas phase reactions between H ₂S and Me ₂ Cd; control of nanoparticle growth, J. Mater. Chem., No. 6,507-09 (1996). Thus, in one embodiment, the gas-phase synthesis can becarried out in the presence of a Lewis base in the gas phase. Forexample, the Lewis base can coordinate to the surface of the QDs andcontrol their size. Higher concentrations of a Lewis base can be used tosynthesize smaller QDs. Suitable Lewis bases may include, but are notrestricted to, pyridine gas. In still another embodiment, thesemiconductor may comprise a material that may act as a Lewis base. Inanother embodiment, the reaction may be carried out at a certaintemperature. Suitable temperatures may include, but are not restrictedto, approximately 25° C. to 200° C. Higher temperatures can be used toproduce smaller QDs. In still another embodiment, a Lewis baseconcentration and temperature are adjusted during gas-phase synthesis inorder to synthesize different size QDs within the semiconductormaterial. In one embodiment, the Lewis base concentration andtemperature can be selectively adjusted to a level that results insynthesis of both red and green QDs within the pores of a semiconductormaterial for a blue-LED (e.g., GaN) at a level that effectivelydown-converts the LED to produce white light emissions.

In an alternative embodiment, QDs having same size but differentwavelength emissions can be grown within the pores of a semiconductormaterial. For example, nanoparticle precursors can be selected to growboth Group III-V based QDs (e.g. InP, and including graded dots andalloys) and CdSe QDs. InP QDs emitting at a particular wavelength arerelatively smaller than CdSe QDs emitting at the same wavelength. Thus,in an embodiment, InP and CdSe QDs can grow to the same size but emitdifferent wavelengths. In one embodiment, the InP and CdSe QDs growwithin pores having uniform diameter, wherein the InP QDs emit red lightand the CdSe QDs emit green light. In an embodiment, the concentrationof precursors for red-emitting QDs and green-emitting QDs can beselectively adjusted to a level that results in synthesis of both redand green QDs within the pores of a semiconductor material for ablue-LED (e.g., GaN) at a level that effectively down-converts the LEDto produce white light emissions.

In one embodiment, a porous semiconductor material 200 is placed in themiddle of two streams of gas flowing from opposite directions, 201 and202, respectively, as illustrated in FIG. 2. The gas streams can includeprecursors to QDs 204. Referring to FIG. 2, as the gas streams flowsthrough the semiconductor material 200, nanoparticle nucleation andgrowth may ensue in the material's pores 203. Nanoparticle sizes can berestricted by the size of the pores 203 they grow in. In an alternativeembodiment, nanoparticle sizes may be restricted by reaction conditions,including adjustment to Lewis base concentration and/or temperature. Inan embodiment, the precursor gas streams flow in an alternating pattern.In another embodiment, the precursor gas streams flow simultaneously.

In another embodiment, a porous semiconductor material 300 is placed inthe stream of two parallel gas sources 301, 302, as illustrated in FIG.3A. The gas streams may be allowed to flow either sequentially or intandem. As in the method described in FIG. 2, the gas streams caninclude precursors to QDs 304. As illustrated in FIG. 3, as the gasstreams flow through the semiconductor material 300, nanoparticlenucleation and growth may ensue in the material's pores 303. Again,nanoparticle sizes can be restricted by the size of the pores 303 theygrow in. In an alternative embodiment, nanoparticle sizes may berestricted by reaction conditions, including adjustment to Lewis baseconcentration and/or temperature. In an embodiment, the precursor gasstreams flow in an alternating pattern. In another embodiment, theprecursor gas streams flow simultaneously.

FIGS. 4 and 5 illustrate embodiments of apparatuses for the gas-phasesynthesis of QDs. In the apparatus 400 illustrated in FIG. 4A, asemiconductor material 401 is inserted into a quartz tube 402, which isthen positioned in a tube furnace 403. QD precursor gasses are providedby lines 404 and 405 to opposite sides of the semiconductor material.The gas streams can flow simultaneously or in an alternating pattern.For example, line 404 may provide a gas phase QD precursor such as H₂S,H₂Se, or PH₃, and line 405 may provide a QD precursor such as R₂Zn,R₂Cd, R₃Ga or R₃In. Apparatus 400 can also include lines 406 and 407 forcarrier gasses. Apparatus 400 may also include a source 408 forproviding a Lewis base. Precursor gas lines may include a reactor 409for generating gaseous precursors. Any or all of the gas lines may beprovided with gas-flow meters 410 and 411. Exhaust lines 412 and 413 maybe provided with scrubbers 414 and 415, respectively, and with pressurecontrollers 416 and 417 respectively.

In the apparatus 500 illustrated in FIG. 5, a semiconductor material 501is positioned into a quartz tube 502, which is positioned in tubefurnace 503. The semiconductor material is exposed to parallel streamsof QD precursor gas provided by lines 504 and 505. The gas streams canflow simultaneously or in an alternating pattern. The apparatus may alsoinclude one or more lines 506 providing additional reagents, such as aLewis base. Lines 504 and 505 are connected to sources of QD precursorgasses 507 and 508, respectively. In apparatus 500, line 506 can beconnected to a source of Lewis base 509. As in the apparatus illustratedin FIG. 4, example precursor gasses for apparatus 500 include H₂S, H₂Se,or PH₃, and R₂Zn, R₂Cd, R₃Ga or R₃In. Any of the gas lines can also beprovided with a source of carrier gas 510 and additional equipment, suchas gas-flow meters 511 and 512. Quartz tube 502 may contain glass wool513 up stream of exhaust line 514. Exhaust line 514 may be equipped withmonitoring, control, or processing equipment, such as one or morescrubbers 515 and pressure controller 516.

The particular set-ups illustrated in FIGS. 4 and 5 are exemplary andschematic only. It will be readily apparent to one of skill in the arthow to implement these and other geometries for providing QD precursorgasses to a semiconductor material, as described herein. The scope ofthe invention is not limited to any particular reactor geometry orapparatus.

The methods and apparatuses described herein can grow QDs within asemiconductor material because gas phase QD precursors can diffuse intonano-size pores and react inside those pores. FIG. 6 compares therelative size of QD precursor molecules Me₂Cd 601, Me₂Zn 602, H₂S 603,H₂Se 604, PH₃ 605, and InMe₃ 606 to the size of O₂ 600.

FIGS. 7A-7C illustrate the formation of QDs within pores selectivelyetched into a semiconductor material 700. Gaseous QD precursors candiffuse into pores as small as 1 nm in width or less. The QD precursorsreact within the pores to form QDs 702. In wider pores 703, theprecursors react to form larger diameter QDs 702 a. In one embodiment,these larger diameter QDs 702 a can emit light that is red-shifted. Innarrower pores 704, smaller diameter QDs 702 b can form. In anotherembodiment, these smaller QDs 702 b can emit green-shifted light.

Referring to FIG. 7A, QDs can be grown in a semiconductor material 700having pores with uniform diameter 710 (FIG. 1A). In another embodiment,as illustrated in FIG. 7B, QDs can be grown in a semiconductor material700 having pores with different diameters 740, 750 (FIG. 1B). In stillanother embodiment, as illustrated in FIG. 7C, QDs can be grown in asemiconductor material 700 having pores with a small diameter 770 in thetop half of the semiconductor material and a large diameter 780 in thebottom half of the semiconductor material (FIG. 1C).

The QD precursors can diffuse into the pores and grow to a size thatfills the diameter of the pores. In one embodiment, the gaseousprecursors include nanoparticle precursors to produce both red 720 andgreen QDs 730 within the uniform-sized pores. For example, the gas mayinclude precursors for Group III-V based QDs (e.g. InP, and includinggraded dots and alloys) and CdSe QDs, which will emit differentwavelengths at a certain size. In an alternative embodiment, adjustingLewis base concentration and/or temperature during synthesis can be usedto selectively control QD size. In one embodiment, reaction conditionsare controlled to grow red-emitting QDs 720 in the bottom half of thesemiconductor material, and green-emitting QDs 730 in the top half ofthe semiconductor material. In yet another embodiment, green andred-emitting QDs are grown within a blue-light emitting semiconductormaterial having uniform pore diameter at a level that effectively downconverts the semiconductor material to white light emissions.

In yet another embodiment, as illustrated in FIG. 8, a conventional LEDcan include a selectively etched n-GaN layer with nanoparticles embeddedin its pores. The LED may include a Sapphire Substrate 801, an n-GaNlayer 802, a p-n junction active layer 803, a p-GaN layer 804, ap-electrode 805, and an n-electrode 806. In one embodiment, both green807 and red-emitting QDs 808 can be embedded in the n-GaN pores. Inanother embodiment, green-emitting QDs 807 are embedded in the top half809 of the n-GaN layer and red-emitting QDs 808 are embedded in thebottom half 810 of the n-GaN layer. Any of these designs can be achievedwith one or more of the aforementioned methods. In still anotherembodiment, the QDs are embedded in the n-GaN layer with a design and ata level that results in down-converting the LED to a substantially whitelight emission 811.

The present application presents numerous advantages over the prior art.It relies on gaseous precursors, which though larger than individualoxygen and water molecules, are of the same order of magnitude. Asillustrated in FIG. 6, the gaseous precursors suggested herein are lessthan three times the length of an oxygen molecule (˜3 Å) along theirlongest axis, which enables them to diffuse into pores less than 1 nm indiameter, i.e. below the lower limit for QD stability. As shown in FIGS.7A-7C, if a pore is large enough such that it corresponds to a diameterwithin the stable QD range, nanoparticle formation may proceed.Furthermore, gaseous precursors are able to penetrate the entiresemiconductor material layer. And unlike prior art techniques such ashigh pressure nitrogen adsorption, the embodiments herein do not assumeand rely on cylindrical pores. The techniques herein can be used toformulate QDs in any pore shape. Furthermore, with the methods andapparatuses described herein, cryogenic temperatures, which may bedamaging to LEDs and may be challenging and costly to maintain, are notrequired. Moreover, the semiconductor need not be exposed to potentiallydamaging high pressures. Consequently, the method does not introducedefects into the semiconductor material during gas-phase synthesis.Furthermore, since the nanoparticle size may be controlled by a numberof parameters, including temperature, time, carrier gas, and theconcentration of an optional Lewis base, the technique may be adaptedfor use with a wide range of semiconductor materials, including thoseused in LEDs.

It's understood that the above description is intended to beillustrative, and not restrictive. The material has been presented toenable any person skilled in the art to make and use the inventiveconcepts described herein, and is provided in the context of particularembodiments, variations of which will be readily apparent to thoseskilled in the art (e.g., some of the disclosed embodiments may be usedin combination with each other). Many other embodiments will be apparentto those of skill in the art upon reviewing the above description. Thescope of the invention therefore should be determined with reference tothe appended claims, along with the full scope of equivalents to whichsuch claims are entitled. In the appended claims, the terms “including”and “in which” are used as the plain-English equivalents of therespective terms “comprising” and “wherein.”

EXAMPLES Example 1 CdS

CdS QDs may be formed from the gas phase reaction of helium gas streamscontaining Me₂Cd and H₂S in the presence of pyridine gas. Typicalreaction conditions include a He flow rate of −600 cm³ min⁻¹ and a30-fold excess of H₂S to Me₂Cd. The particle size may be controlled byvarying the pyridine concentration and/or the reaction temperature.Preferably, pyridine:Me₂Cd ratios in the range 1:20 to 2:1, andtemperatures between room temperature and 200° C. are employed. It hasbeen found that increasing the pyridine concentration reduces theparticle size, while the particle size increases with increasingtemperature.

The absorption of the CdS nanoparticles may be tuned from the UV to cyan(bulk band gap ˜512 nm) depending on the particle size. For example,nanoparticles in the size range 2-20 nm may be expected to emit betweenapproximately 320-500 nm, corresponding with UV to cyan light.

Example 2 CdSe

Reaction conditions similar to those outlined for CdS (above) may beused to synthesize CdSe QDs [N. L. Pickett et al., J. Mater. Chem.,1997, 7, 1855], substituting H₂S for H₂Se. Higher pyridineconcentrations may be used to control the particle size (up to 150:1pyridine:Me₂Cd).

The absorption of the CdSe nanoparticles may be tuned from the blue tothe deep red (bulk band gap ˜717 nm) depending on the particle size.Nanoparticles in the size range 2-20 nm may be expected to emit betweenapproximately 490-700 nm, corresponding with blue to deep red light.

Example 3 ZnS

Reaction conditions similar to those outlined for CdS (above) may beused to synthesize ZnS QDs [N. L. Pickett et al., J. Mater. Chem., 1997,7, 1855], substituting Me₂Cd for Me₂Zn. Higher reaction temperatures (upto 300° C.) may be advantageous.

The absorption of the ZnS nanoparticles may be tuned across the UVspectrum (bulk band gap ˜344 nm) depending on the particle size.Nanoparticles in the size range 2-20 nm may be expected to emit betweenapproximately 235-340 nm.

Example 4 ZnSe

Reaction conditions similar to those outlined for ZnS (above) may beused to synthesize ZnSe QDs [N. L. Pickett et al., J. Mater. Chem.,1997, 7, 1855], substituting H₂S for H₂Se. A reducing H₂ carrier gas,rather than inert He, may be more effective at controlling the particlesize.

The absorption of the ZnS nanoparticles may be tuned from the UV to theblue (bulk band gap ˜459 nm) depending on the particle size.Nanoparticles in the size range 2-20 nm may be expected to emit betweenapproximately 295-455 nm, corresponding with UV to indigo light.

Example 5 InP

InP nanoparticles may be synthesized using a reaction procedure similarto those outlined for II-VI QDs (above) from Me₃In and PH₃ gaseousprecursors.

The absorption of the InP nanoparticles may be tuned from the green tothe near-IR (bulk band gap ˜925 nm) depending on the particle size.Nanoparticles in the size range 2-20 nm may be expected to emit betweenapproximately 520-875 nm, corresponding with green light to IRradiation.

What is claimed is:
 1. A composition comprising: a light-emitting semiconductor material having pores therein; and quantum dots (QDs) disposed within the pores; wherein the composition is free of solvent.
 2. The composition of claim 1, wherein the pores are about 2 nm to about 10 nm in diameter.
 3. The composition of claim 1, wherein the light-emitting semiconductor material comprises as GaN, AlGaAs, AlGaInP, or AlGaInN, or any derivatives thereof.
 4. The composition of claim 1, wherein the QDs comprise a semiconductor material selected from CdS, CdSe, ZnS, ZnSe InP, GaP Cd₃P₂ and In₂Se₃.
 5. The composition of claim 1, wherein the QDs have diameters essentially equal to the diameters of the pores.
 6. The composition of claim 1, wherein the QDs emit green light when illuminated by light from the light-emitting semiconductor.
 7. The composition of claim 1, wherein the QDs emit red light when illuminated by light from the light-emitting semiconductor.
 8. A light emitting device, comprising: a light-emitting semiconductor material having pores therein; and quantum dots (QDs) disposed within the pores; wherein the composition is free of solvent.
 9. The device of claim 8, wherein the pores are about 2 nm to about 10 nm in diameter.
 10. The device of claim 8, wherein the light-emitting semiconductor material comprises as GaN, AlGaAs, AlGaInP, or AlGaInN, or any derivatives thereof.
 11. The device of claim 8, wherein the QDs comprise a semiconductor material selected from CdS, CdSe, ZnS, ZnSe InP, GaP Cd₃P₂ and In₂Se₃.
 12. The device of claim 8, wherein the QDs emit green light when illuminated by light from the light-emitting semiconductor.
 13. A method for synthesizing QDs in a light-emitting semiconductor material, the method comprising: flowing gaseous QD precursors through pores in a semiconductor material to effect reaction of the QD precursors in the absence of liquid solvent.
 14. The method of claim 13, wherein the pores are about 2 nm to about 10 nm in diameter.
 15. The method of claim 13, wherein the light-emitting semiconductor material comprises as GaN, AlGaAs, AlGaInP, or AlGaInN, or any derivatives thereof.
 16. The method of claim 13, wherein the QDs comprise a semiconductor material selected from CdS, CdSe, ZnS, ZnSe InP, GaP Cd₃P₂ and In₂Se₃.
 17. The method of claim 13, wherein the QDs have diameters essentially equal to the diameters of the pores. 